Much recent work in realistic image synthesis has focused on the use of actual data measurements of a surface of three-dimensional object for rendering said surface with parametric texture maps in a computer graphics system.
One conventional method consists to characterize the reflectance properties of a surface by its bidirectional reflectance distribution function (BRDF), as explained in the document “Geometric Considerations and Nomenclature for Reflectance”, U.S. Department of Commerce, National Bureau of Standards, published in October 1977 and written by Nicodemus, F. E., Richmond, J. C., and Hsia, J. J. One known technique for measuring the BRDF of a surface is image based and consists to photograph a surface under varying lighting conditions so as to determine a bidirectional reflectance distribution of the surface. In particular, the document “Polynomial Texture Maps”, published in 2001 and written by Malzbender, T., Gelb, D., and Wolters, H., relates to an apparatus for in situ surface reflectance measurement, wherein 50 inward-pointing light sources are distributed on a small, portable hemispherical frame, each light source illuminating the surface from a different known direction and a camera positioned at the apex of the hemispherical frame capturing the light reflected by the surface.
However, this later solution raises several problems. Firstly, the accuracy of the parametric texture map is directly dependent on the number of light sources of the hemispherical frame. A great number of light sources are thus needed to get a sufficient accuracy. Furthermore, this accuracy is not always possible considering that one light source may deliver a light slightly different from another one. The measurements made by the camera must thus be corrected afterwards by the computer graphics system to correct this lack of homogeneity. Finally, in this solution, the positions of the light sources on the periphery of the hemispherical surface are predetermined and can not be modified. Therefore, the modification of the incident direction of the light sources can not be made or made only by providing other hemispherical surfaces comprising other locations for the light sources corresponding to other incident directions thereof.
A need therefore exists to develop a device for determining a bidirectional reflectance distribution function of a subject which overcomes the deficiencies of the above mentioned device.